Air flow proportioning apparatus



United States Patent O 3,413,998 AIR FLOW PROPORTIONING APPARATUS ArthurS. Vaughan, Mllburn, NJ., assignor to Foster Wheeler Corporation,Livingston, NJ., a corporation of New York Filed May 5, 1965, Ser. No.453,461 5 Claims. (Cl. 137-118) ABSTRACT OF THE DISCLOSURE An air flowproportioning apparatus utilizing two venturis with throats ofsubstantially equal cross-sectional area and means actuated by thepressure drops across said venturis for opening and closing dampers inaccordance with a predetermined rate of ow.

As the trend toward larger and larger steam generators continues, it isessential to resort to opposed ring of the steam generators with opposedburner banks. With opposed fring, it is often essential to proportionthe flow of air to the two separate banks.

Therefore, it is an object of this invention to provide an apparatus forproportioning any given total air ow into two separate ows.

In accordance 'with this invention, two virtually identical venturis areeach located in a separate duct. A separate damper is located downstreamfrom each venturi. A system is provided to control the operation of thedampers which is actuated by the pressure drop across the venturis.

The invention may be better understood from the following detaileddescription considered in conjunction with the accompanying drawingwhich is a schematic diagram of the apparatus.

Referring now to the drawing, a furnace 11 has a front side 13 and arear side 15. Located at the front side 13 is a group of front burners17, and located at the rear side 15 is a group of rear burners 19. Airis supplied to the front burners 17 by a front duct 21. Similarly, airis supplied to the rear burners 19, by a rear duct 23. The air issupplied to the front duct 21 and the rear duct 23 from a fan 25 orother source of air which is most usually connected to the front duct 21and rear duct 23 through a main duct 27.

Located Within the front duct 21 is a front venturi 29. Similarly, arear venturi 31 is located within the rear duct 23. It should be alsonoted that it is advisable that both the front venturi 29 and the rearventuri 31, which are virtually identical in shape and size, beapproximately the same distance from the source of air 25.

Within the front duct 21 a short distance downstream of the frontventuri 29 away from the fan 2S is a front damper 33. Downstream of therear venturi 31 is a rear damper 35.

A front throat tube 37 senses the pressure at the throat of the frontventuri 29 while a front upstream tube 39 senses the pressure enteringthe front venturi 29. These two pressure signals from the front venturi29 are relayed to a front, low-differential pressure transmitter 32which determines the diiferential in pressure between the throat and theentrance of the front venturi 29. The front, low differential pressuretransmitter 32 transmits this differential as a front, low-differentialsignal through a tube 41. Similarly, a rear throat tube 43 senses thepressure at the throat of the rear venturi 31 While a rear upstream tube45 senses the pressure entering the rear venturi 31. These two pressuresignals from the rear venturi 31 are relayed to a rear, low-differentialpressure transmitter 47 which determines the differential in pressurebetween the throat and the entrance to the rear venturi 31. The rearlow-differential pressure transmitter 47 determines the dif- 3,413,998Patented Dec. 3, 1968 ice ferential between the throat and entrance andtransmits this differential as a rear, low-differential pressure signalthrough a tube 49.

The front, low-dierential signal is transmitted through the tube 41 to adiaphragm 51 of a computing relay 53. The rear, low-differential signalis transmitted through the tube 49 to the opposite side of the diaphragm51. A permanent pressure, preferably 9 p.s.i., is applied to thediaphragm 51 by a spring 55. Thus, when the front, lowdifferentialsignal and the rear, low-differential signal are equal, the computingrelay 53 will transmit a 9 p.s.i. pneumatic signal through the tube 57to a proportional and reset controller 59. The predetermined extent ofproportioning of ilow between the front duct 21 and the rear duct 23 ismanually applied through a manual loader 61. The manual loader 61transmits a load signal to the proportional and reset controller 59through a tube 63. The proportional and reset controller 59 combines thesignals into a control signal which is fed to a front pneumatic actuator65, and a rear pneumatic actuator 67, through a tube 69. Located alongthe tube 69 is an auto-manual control station 71 which permits manualoperation of the front and rear pneumatic actuators 65, 67 withoutoperation of the previously described pneumatic system. The frontpneumatic actuator is mechanically connected to the front damper 33while the rear pneumatic actuator 67 is connected to the rear damper 35.

One of the two pneumatic actuators 65, 67 is adapted to close itsrespective damper at 3 p.s.i. and open it at 9 p.s.i. The otherpneumatic actuator is adapted to close its respective damper at 15p.s.i. and open it at 9 p.s.i. Thus, only one damper can be partially ortotally closed and the other damper must be open to limit the amount ofpressure drop that can be caused by the dampers.

The symbol S is used on the drawing to indicate that supply air is beingfed to the respective piece of equipment.

Since partial closing of one damperI increases the flow resistance tothe total flow, the fan output must be increased under thesecircumstances. Therefore, the abovedescribed pneumatic system must beinterconnected with the air-flow control system. Accordingly, a tube 73is connected to the tube 41 and a tube 75 is connected to the tube 49.In this way, the front, low-differential signal and the rear,low-differential signal are transmitted to an airow totalizer 77 whichin turn sends a total air-flow signal through Va tube 79 to thecombustion control system 81. Generally, the combustion control systemoperates a pneumatic fan actuator 83 through a tube 85 which opens andcloses a shutter 87 of the fan 25.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. An apparatus for proportioning the air ow to a furnace between thefront burner bank and the rear burner bank, comprising:

a source of pressurized air;

a front duct connected to said source of pressurized air;

a rear duct connected to said source of pressurized air, said front ductand said rear duct being of equal cross-sectional area;

a front venturi located in said front duct;

a rear venturi located in said rear duct, said front and rear venturishaving throats with equal cross-sectional areas;

a front damper located downstream of said front venturi in said frontduct and adapted to be opened and closed to control the flow of airthrough said front duct;

a rear damper located downstream of said rear venturi in said rear ductand adapted to be opened and closed to control the ow of air throughsaid rear duct; and

means actuated by the pressure drops across said venturis for openingand closing said dampers in accordance with a predetermined proportionalrate of 5. An apparatus for proportioning air ow to a furnace betweenthe front burner bank and the rear burner bank comprising:

a source of pressurized air;

llow between the front and rear ducts, said means for opening andclosing said `dampers opening and closing said front and `rear damperssuch that one of said dampers is wide open at all times. 2. Anappa-ratus according to claim 1 wherein said a front duct connected tosaid source of pressurized means for opening and closing said dampers ispneumatic. air;

3. An apparatus according to claim 1 `wherein said a rear duct connectedto said source of pressurized means for opening and closing said dampersincludes: air, said front duct and said rear duct being of submeans fordetermining the difference in pressure drop stantially equalcross-sectional area;

across the front venturi and the rear venturi and afront venturi locatedin said front duct; converting the difference into a first signal; arear venturi located in said rear duct, said front and means forcomparing the rst signal with a predeterrear venturis having throatswith equal cross-sectional mined signal and forming a second signal; andareas; actuating means mechanically connected to said front 2 a frontdamper located downstream of said front and rear dampers and adapted tobe operated by venturi in said front duct and adapted to be opened saidsecond signal. and closed to control the ow of air through said 4. Anapparatus according to claim 1 wherein said front duct; means foropening and closing said dampers includes; a rear damper locateddownstream of said rear venturi a front, pneumatically-operated,low-differential presin said rear duct and adapted to be opened andclosed sure transmitter connected to said front venturi and t0 COIltrOlthe OW Of air llhrOugh Said rear duct; adapted to transmit as apneumatic signal the pressure a front means connected to said frontventuri to transditerential across said front venturi; mit the pressuredifferential across said front venturi; a rear, pneumatically-operated,low-differential presa rear means connected to said rear venturi totranssure transmitter connected to said rear venturi and mit thepressure different acoss said rear venturi; adapted to transmit as apneumatic signal the pres` a computing relay means connected to bothsaid front sure differential across said rear venturi; means and saidrear means to compare the signal a pneumatically-operated differentialcomputing relay from the front means and the signal from the rearconnected to both said front, pneumatically-operated, means and totransmit a signal representing that low-differential pressuretransmitter and said rear, COIIlPariSOIl; pneumatically-operated,low-differential pressure a proportional and reset controller means toreceive transmitter and adapted to compare the pneumatic signal from thefront, pneumatically-operated, lowdifferential pressure transmitter andthe pneumatic signal from the rear, pneumatically-operated,lowdiierential pressure transmitter and to transmit a pneumatic signalrepresenting that comparison;

the signal from said computing relay means;

a loader means to transmit a signal in accordance with a predeterminedproportioning of the air ow to said proportional and reset controllermeans, said proportional and reset controller means being adapted totransmit a signal representing the signals from said computing relaysand said loader means; and

means to actuate in accordance with the signal from the proportional andreset controller means the front damper and the rear damper such that atleast one damper is maintained wide open at all times.

References Cited UNITED STATES PATENTS controller being connected withsaid manual loader 1 206 806 12/1916 Borden 137 g7 and adapted toreceive the pneumatic signal from 1620240 3/1927 Smoot 1379g X saidmanual loader and transmit a signal represent- 2395384 2/1946 Ziebolz137 98 X ing the signals from said pneumatically-Operated dif- 3103228 9/1963 Davenport 137 93 ferential computing relay and said manual loader;and FOREIGN PATENTS a pair of pneumatically-operated actuators, one of843,621 3/ 1939 France,

which is mechanically connected to said front damper and the other ofwhich is mechanically connected to said rear damper and both of whichare pneu- WILLIAM F. ODEA, Primary Examiner.

D. I. ZOBKIW, Assistant Examiner.

